1. Field of the Invention
The present invention relates to a controller for drivingly controlling servomotors that are used to drive feed axes of a machine tool table, etc., and more particularly, to a servomotor driving controller for suppressing formation of a projection on a machined surface of a workpiece in the process of machining the workpiece attached to a table upon reversal of the moving direction of a feed axis of the table.
2. Description of Related Art
In a machine tool or the like, upon reversal of the driving direction of a servomotor which drives a feed axis of a machine tool table, the table cannot immediately be reversed due to backlash of a feed screw and friction. Therefore, in the process of for example circular arc cutting a workpiece mounted to the table, a projection is formed on the circular arc cutting surface of the workpiece when the driving direction is reversed.
It is assumed here that the workpiece mounted to the table to be movable in an XY coordinate plane is subject to circular arc cutting, with the circular arc center positioned at the coordinate origin and with the X and Y axes moved in the positive and negative directions, respectively, and there occurs a quadrant change such that the Y axis is kept moved in the negative direction but the moving direction of the X axis is changed from positive to negative. Upon such quadrant change, the Y axis is kept driven at the same driving velocity, whereas the X axis attempts to reverse the moving direction when the positional deviation is reduced to zero and the torque command becomes small. However, immediate reversal cannot be realized due to the presence of friction. Moreover, attributable to backlash of the feed screw, the table movement in the X axis direction is delayed when the moving direction of the X axis is reversed. In this manner, there occurs a delay in direction reversal upon quadrant change, and as a result, a projection is formed in the cutting surface, which projection will be referred to as quadrant projection.
In order to reduce the quadrant projection, various correction methods have been proposed (see, for example, JP 7-110717A).
However, these proposed methods making adjustments of a correction amount added for reduction of quadrant projection while confirming results of the corrections require much time for adjustments.